Maximum Circuit Length
Longest run allowed by fault loop and voltage drop.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the maximum circuit length tool do?
The tool reports two lengths. The first is the route length that still allows the protective device to disconnect in time. The second is the length at which the voltage drop reaches your limit. The shorter of the two governs the run.
Where do the two lengths come from?
The fault loop length comes from AS/NZS 3000:2018 Table B1 for a 0.4 s disconnection time at 230 V, scaled by your nominal voltage. The voltage drop length uses the resistance and reactance from AS/NZS 3008.1.2:2017 Tables 30, 34 and 35, against Clause 3.6.2.
Why does a combination show no fault loop length?
Table B1 tabulates a fixed list of conductor pairs and device ratings. A pair that is not printed has no tabulated length, so the tool reports the voltage drop length only. Use the loop impedance tool to check that combination instead.